Adsorption of Silane Coupling Agents on Glass Fibre Surfaces

Commercial glass fibres are commonly used in reinforced composites. The importance of such composites is apparent in a number of areas and applications. Composites have maintained their popularity during several decades, as the products offered give both strength and modulus at a reduced weight. Glass fibres used in composites are almost always pre-treated with coupling agents. Coupling agents are capable of interacting with both the organic polymer resin as well as the inorganic glass surface. These coupling agents play a key role in the strength of a composite. The overall objective of this work was to characterize glass fibre surfaces after surface treatment with silane and to gain better understanding of surface processes at the silane-glass interface of a composite. Another goal was to investigate how the solvent used in the surface treatment process affected silane adsorption on the glass fibre surface. Adsorption of silane coupling agents from water and organic media on a glass fibre surface were determined with several analysis methods. The results indicate that adsorption is dependent on different factors affecting the monomer dispersion and the formation of a polymer layer on the glass fibre surface. If the silane adsorbs only physically on the fibre surface it can lead to a break in the reinforced product. In order to avoid a breakage the silane treatment must be performed in a way, that only chemical adsorption of the silane can take place on the fibre surface. In this study, adsorption mechanisms of silanes on both pure silica powders as well as glass fibre surfaces were examined. The experimental adsorption processes on a silica powder could be described by a combination of the Henry and Langmuir adsorption isotherms. Important information on changes in electrokinetic parameters of heterogeneous glass fibre surfaces was obtained with streaming potential measurements. The changes introduced by silane adsorption on glass fibre surface affected the streaming potential and a clear change in the surface charge was detected. The adsorption was further confirmed by ESCA measurements by following the carbonyl C3 signal. Information of the pH dependence of adsorption was detected by streaming potential measurements. Furthermore, it was found that treatment of glass fibres with acids and bases resulted in leaching ions from both the fibre surface as well as from the fibre bulk. Part of the ions being leached out from the glass fibre surface were replaced by ions originating from the bulk of the fibre. This created an ion gradient from the fibre bulk to the surface